Signaling system



May 19, 1942. w, cox 2,283,415

SIGNALING SYSTEM Filed Feb. 6, 1941 Pink/m? INVENTbR; JOHN M COX flTTOR/VEY Patented May 19,1942

' sTAr SIGN G SYSTEM John W. Cox, Berkeley, Calif assignor to Radio Corporation of America, a corporation oi Delaware Application February 6, 1941, Serial No. 377,608

3 Claims. (Q1. lift-6.6)

This invention relates to telegraph signaling systems and will be described in connection with constant frequency variable dot facsimile and Otherobjects of the invention will appear in the following description, reference being had-to the drawing, in which:

Fig. 1 is a diagrammatic illustration of the receiving circuits embodying my invention.

Fig.2 is a graph of the CFVD signals converted into tone signals.

Fig. 3 illustrates graphs of the potentials apall this is well known in the art andis not illustrated. Reference is made to the. patent to Henry Shore and James N. Whitaker, No. 2,083,245, granted June 8, 1937, for such a prior art system.

It is assumed that the CFVD signals in the form of tone signals are received in the primary of transformer I at the recording oflice. These signals are of the form shown at 2 in Fig. 2. The distances between .the centers of these s als are uniform and hence have a constant dot frequency. They, however, are of varying length.

The secondary of the transformer is'connected through rectifier 3 to load resi tance 4 and smoothing condenser E. Condenser 6 is adjust- I 'ably connected to resistance 4 and is shunted by a variable high resistance 1 to vary its time conto condensenfi and it may include a negative biasing source 9 to cause operation along the proper part of the grid voltage-plate current characteristic. The cathode is connected to ground, which is the negative terminalof the or plate supply. i

The plate of tube 8 is connected to the positive terminal of the B source through a neon tube Ill and the primary of transformer II in series rela tion. A resistance I2 is shown in this circuit {or control purposes. A condenser i3 shunts the primary and the neon.tube.' The vacuum tube 8,

mean tube iii and condenser I3 constitute an oscillator, as will later be described.

. The secondary of transformer II is connected to a frequency demodulator It consisting ot a low-pass filter, though a high-passer band-pass filter, or any other' demodulator, could equally well be used. This filter shown consists of series inductance and shunt capacity.

' The output of demodulator It is connected to rectifier i5 and load resistance I5, acrosswhich is connected a smoothing condenser I'l, though this is not essential. 'A recorder. i8 is adjustably 25 plied to the grid of the amplifier tube after the Y tone currents arerectified and filtered.

connected across resistance It. This may be any type of amplitude recorder; for example, a photo recorder producing a record from a lamp fed a well-knowntype.

The operation follows:

The CFVD signals arrive as tone frequency at with the current of varying amplitude, which is,

of my improved system is as transformer I, in the form indicated at 2 in Fig.

2. The current is rectified and smoothed out'to produce a negative potential in the input circuit of tube 8, as indicated at I9. This is added to whatever constant negative bias 2!) is applied by the source 9.

The varying signal potential produced by the 40 CFVD signals is integrated by condenser 6 and high resistance I, so that a total average potential for the signals assumed, is produced as shown at 2|.

plate-cathodeimpedance in tube 8, which is in 5 series with the charging circuit of condenser I3.

Condenser l3 charges and when the potential reaches the striking value of neon tube III, the condenser discharges through that tube. It continually charges and discharges, thus producing a currentv having a frequency set by the variable impedance of tube 8. When theimpedance of that tube is high, the condenser will charge more slowly and when it is low, it will charge more rapidly. Hence, the varying negative potential stant. The input circuit of tube 8 is connected p oducedby the CFVD signals will cause the This produces a varying internal.

frequency, as indicated at 22 in Fig. 4.

about: condenser and neon tube to oscillate at a varying The voltage of varying frequency passes into 1 a screening effect. I have found 2,000 cycles per second to be a satisfactory frequency.

There is a further advantage in the use of my invention in that static clicks occurring in the spaces will not be recorded, because they are of too short duration to produce a noticeable change in the frequency of the oscillator.

A further advantage in my invention is that the filter demodulator can be warped in its frequency characteristic in any way desired and by proper design of inductance and capacity, detail in the near black portions of the picture can be readily obtained. Detail in this portion of the picture cannot be satisfactorily obtained by recording the CFVD signals directly. I

In CFVD transmission, it has been found advisabl to use 10% dots for white, which will not record as pure white. By using myinvention, the 10% dots are too short to produce a frequency in the oscillator output that will pass the demodulator and hence pure white will be produced by the recorder. My improvement has like advantages when signals of other dot percentages are used.

If desired, the condenser-neon tube oscillator may be located at the receiving station and the variable frequency produced will then make it unnecessary to use tone frequency for the transmission to the recorder. This can b accomplished with a very narrow frequency band width.

In doing this, I have used a band that is only approximately cycles in width from black to white. The standard CFVD system requires a much wider tone frequency band.

In the modification of Fig. 5, the condenser 5 of Fig. 2 has been omitted and an extra resistance 4' inserted in the grid conductor. This will produce the same results as Fig. 2.

It will be apparent that various modifications may be made in my invention without departing from the spirit of the invention.

' Having described my invention, what I claim is:

I. In facsimile reception of current signals. of constant frequency and variable time length,

-means for receiving said signalameans for converting the signals-into'alternating current having a frequency varying with the time length of the signals, means for converting the variable frequency current into current of varying amplitude, and means for recording the last-mentioned current.

2. In facsimile reception of current signals of constant frequency and variable time length, means for receiving said signals, means for converting the signals into alternating currenthaving a frequency varying with the time length of the signals, means for converting the variable frequency current into alternating current of,

varying amplitude, means for rectifying said alternating current and means for recording said rectified current. I

3. In" facsimile reception of current signals of constant frequency and variable time length, means for receiving said signals, an oscillator, means for varying the frequency of said oscilla- ,torwith the time length of the signals, a reactance circuit for passing said varying frequency with amplitudes varying with the frequency, a rectifier for said current of varying amplitude and means for recording the rectified current.

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